The primary issues associated with implementation of fuel cell vehicles and the like are in manufacturing components at rates compatible with vehicle production, and at costs that can be borne by the consumer and industry. Current high-pressure storage cylinders need to be carbon composite due to the weight penalty associated with metallic tanks. However, current state-of-the-art in composite cylinder production relies on filament winding of either wet fiber tows, or of a pre-preg fiber with pre-impregnated resins (typically epoxy or possibly other thermoset and some thermoplastic resins.) These are wound onto a liner with precise control of fiber orientation to allow optimum stress fields, and the overall wound cylinder is typically placed in an oven or autoclave and cured for some period of time. The typical process sequence can take from 4-8 hours per cylinder, and for example, as referenced by Iida et al (U.S. Pat. No. 6,190,481) a cure time of over 6 hours was demonstrated for tank manufacture. The state of the art is further reflected in patent literature such as Goldsworthy et al (U.S. Pat. No. 6,565,793) and more recently Iida et al (U.S. Pat. No. 7,032,769).
In order to be compatible with vehicle production rates, a process that is approximately 20 minutes or less is desirable. In the above referenced state-of-the-art, from 12 to 24 different tools and process lines are necessary for the parallel processing required to reach 20 minute product cycle times. This is capital, labor, and space intensive, and is not optimum for real-world production requirements. The current status has been verified by recent private communication with a major automotive manufacturer.
Attempts have been made to modify other composite processes to take advantage of faster cycle time, including using resin transfer molding into a dry-fiber preform which is filament wound onto a cylinder liner. The issues with these approaches have come from holding appropriate tension on the fibers after wrapping, with holding net-shape on the carbon wrapped liner so that mold closure does not wrinkle the carbon fibers and thus knock down the properties to unacceptable levels, and with rapid and repeatable injection processes. The latter is a key factor as the existing systems have typically used heat and pressure transfer via the mold external surface, and utilizing pressure control via injection pressure of the resin.